Enterobius Vermicularis - Pinworm

Human pinworm, Enterobius vermicularis, is the most common parasitic worm infection in the United
States and Western Europe. Pinworms are easily transmitted from human to human and are particularly common in
children. Luckily the disease, enterobiasis, causes only anal itching.

Enterobius vermicularis does not need an intermediate host to complete its life cycle.
Humans get infected by accidentally swallowing or inhaling microscopic pinworm eggs. Once inside the first part of
the small intestine, duodenum, pinworm larvae hatch from the eggs. The larvae are only about 0.15 mm long but grow
very fast. They migrate towards the ending of the small intestine as they mature into adults. Adults are white,
thin worms. Males are 0.2 mm thick and 2–5 mm long whereas females are 0.5 mm thick and 8–13 mm long. Life
expectancy for males is seven weeks whereas females live 5–13 weeks. The males usually die after the pinworms have
mated in the last part of the small intestine, ileum. The gravid (pregnant) female resides at the beginning of the
large intestine, colon, eating what ever food passes through the intestinal tract. Female pinworm reaches fertility
within four weeks. She swims at the rate of 12 cm per hour towards the rectum. During sleep when body temperature
is low and there is less movement the female pushes out from the anus and lays eggs on the outside skin. The eggs
get stuck on skin, underwear or bedding and become infective within a few hours. Eggs survive up to three weeks on
clothing, sheets or other objects. After the female has laid 11000–16000 eggs it dies.

Sometimes pinworms lay eggs inside the colon. If the eggs are not taken out in the feces the larvae might have
enough time to hatch. This can only happen in the large intestine or rectum and only if enough oxygen is present.
The larvae migrate back up the intestinal tract and develop into adults. This is very rare but happens every now
and then.

Diagnosis is made by identifying pinworms or their eggs. Worms can sometimes be seen on the
skin around the anus 2–3 hours after falling asleep. Eggs can be collected using a transparent cellophane tape by
pressing the sticky side of the tape to the anal skin. The eggs stick to the tape which can be placed on a slide
and examined under a microscope by a doctor. Bathing or having a bowel movement can remove eggs from the skin. So
this test should be done immediately after waking up. It needs to be repeated on the following two mornings to
increase the chance of finding pinworm eggs.

Enterobiasis can be treated with either prescription or over-the-counter medications. A health
care provider should be consulted before treating a suspected infection. Some common drugs against pinworms are
albendazole and mebendazole. The drugs kill larvae and adults but not the eggs. To get rid of all pinworms another
dose needs to be taken after two weeks to kill the newly hatched larvae. All family members should be treated at
the same time. If children are in close contact with other children, like in kindergarten, then there is a
possibility that other families are infected, too. The least embarrassing way to handle the situation is to only
tell the kindergarten teacher. She will inform the other parents that their children might have pinworms and should
be treated with the drug.

To prevent new infections always keep fingers out of your mouth and nose. Keep fingernails
short and do not bite your nails. Wash your hands after using the toilet and before eating or preparing food.
Change clothing, towels, and sheets frequently and wash them in hot water, especially during and after pinworm
treatment. If you have pets, keep them clean. The human pinworm, Enterobius vermicularis, does not infect
other animals but pets can carry eggs in their fur.